Escaping ammonia gases and the resultant fumes therefrom have long plagued the diazo-type copying apparatus art. Various methods have been suggested and tried in an effort to eliminate this problem. One method, disclosed in U.S. Pat. No. 1,760,149, was to place a perforated vacuum tube beneath an external copy collector tray of a developer. This met with some success, but since the vacuum tube was in contact with only one side of the copy produced, ammonia gas could escape from the opposite side of the copy. In addition, the vacuum was not applied until after the copy was exposed to the atmosphere external of the copier thereby affording the ammonia gas a chance to escape before the vacuum could even expel the ammonia gases from one side of the copy.
Another suggested method to prevent the escape of ammonia gases from a diazo-type copier is disclosed in U.S. Pat. No. 3,720,150. This patent discloses an alternate pressure vacuum channel system within the walls of the copier entrance and exit slots. At the points where the copy enters and exits, the copy is subjected to a pressure force which creates a barrier or back pressure to prevent ammonia gases from escaping the developing chamber and then the copy is subjected to a vacuum which collects any ammonia gas which remains on the copy or which may have escaped the developing chamber, but as yet had not reached the external atmosphere. While this method is effective in reducing the amount of ammonia gases that escape to the atmosphere, it requires two sets of vacuum channels and two sets of pressure channels in both the entrance and exit slots.
A third method which has been suggested in U.S. Pat. No. 3,900,862, discloses a vacuum chamber that operates at subatmospheric pressure, thereby eliminating the escape of ammonia gases from the developing chamber to the atmosphere. Escape is eliminated due to the differential between the atmospheric pressure and the subatmospheric pressure in the developing chamber, thereby forcing the surrounding atmosphere into the developing chamber as opposed to allowing the ammonia gases to escape the developing chamber. This, however, requires a large vacuum pump to maintain an area as large as a developing chamber at subatmospheric pressure.
Numerous methods have been tried to mechanically improve the seals located at the entrance and exit slots of the developing chamber, but without as much success as the use of vacuum seals.
In addition to containing the ammonia gases by one or more of the above methods, there is also the additional problem of eliminating the gases. The prior art discloses various ways of neutralizing the ammonia gases such as subjecting them to liquid absorbing solutions, filters containing ammonia absorbers, cartridges containing ammonia absorbing pellets and catalytic converters.
It is accordingly an object of the present invention to reduce the amount of ammonia gases and fumes that have a tendency to escape the developing chambers of diazo-type copiers without the resulting problems of the prior art.